(Also posted on forums.debian.net; hopefully that's not bad etiquette, I'm unclear on the relationship between the two boards)

I just installed stretch on a new machine (Ryzen 5 2600 / AMD RX 570 GPU / AsRock B450-M Pro / Samsung 43NU6950 display), and am having various display driver-related (I think) difficulties with appropriate modelines and with having no sound (over HDMI or otherwise):

* Initially X ran at a max resolution of 1920x1080, and refused explicit modelines suitable for the 4K monitor. AFAICT by inspecting Xorg.0.log, it tried running the radeon driver, which apparently doesn't support the Polaris 12 GPU in my RX 570, and fell back to the VESA driver.* To get around this I installed the AMDGPU driver, e.g. just installed linux-firmware. This did succeed in running at 4K, but the system has no sound. Apparently AMDGPU doesn't support sound over HDMI until the DC improvements consequent to kernel 4.15 and later, but that aside, I wasn't even getting sound out of the onboard analog audio ports, and no audio device showed in the audio controls other than "Simultaneous Audio" without any underlying physical devices.* This seemed odd because the snd_hda_intel module was loaded, and there were no obvious audio-related errors in syslog. All I see is:

That's where matters stand. If I could get analog audio out, that would be something, but I'd like audio over HDMI. Advice welcome; possible paths forward I see right now are:

* Try the AMDGPU-PRO driver, which supposedly doesn't have the audio-over-HDMI issue (whether this would address the underlying complete lack of audio problem is not clear to me). * Update to testing, which supports a kernel recent enough that it might support the DC layer improvements needed for AMDGPU audio-over-HDMI (again, whether this has any bearing on the lack of analog audio is unclear). I'm averse to doing this since this is intended to be my primary desktop / production system.

The audio issue might be simple. I do not know if it is still the case, but back when I used Debian the default audio settings had mute enabled. A new installation required changing the mute setting to off.

btw: back in the days it was possible to install a kernel from testing or sid without running into problems. It was one of the very few exceptions to the general rule to never ever mix stable with anything but stable-backports.backporting it yourself is probably preferred anyway.But, as said, i don't even think that debian-backports won't offer a kernel new enough.

Thanks. I updated to the 4.18.0 kernel and corresponding firmware-amd-graphics in stretch-backports (and a bunch of other stuff that got pulled in by apt upgrade), and my video problems seem largely solved. Unfortunately I'm still getting no audio. There are two alsa devices for the ATI HDMI and Realtek, but neither seems to be producing sound. I'm unclear how to begin diagnosing this further given my very small knowledge of audio issues.